Various techniques are used to measure formation properties, such as transient electromagnetic (EM) induction measurement techniques. Transient EM methods such as deep transient logging while drilling (LWD) and measurement while drilling (MWD), especially using “look-ahead” capability, have been shown to have great use in geologic formation evaluation and measurement. Transient EM techniques involve disposing a tool including at least one transmitter and receiver, and transmitting transient pulses of current into a formation. The induced electromagnetic field and decay responses are measured. Transient EM measurements can be used for various purposes, such as estimation of the electrical conductivity of earth formations surrounding a borehole. Transient EM measurements may also be used for geo-steering, e.g., by identifying formation boundaries.
There are several factors that pose challenges to performing both geo-steering and ahead of the bit induction measurements while drilling. One factor is the electrically conductive drill string (e.g., metal pipe). The measured transient induction signal is severally affected by eddy currents that develop in the drill string and limit resolution of measurements of formation parameters, for example, measurements of a water-oil boundary in the case of geo-steering.